An organic light emitting device is an electronic device including an anode, a cathode, and an organic compound layer disposed between both the electrodes. Holes and electrons to be injected from the respective electrodes recombine with each other in the organic compound layer (in particular, light emitting layer). When excitons generated by the recombination return to the ground state, the organic light emitting device emits light.
Recent advances in the organic light emitting device are remarkable, and have resulted in the following features, for example. That is, the organic light emitting device has a low driving voltage, a variety of emission wavelengths, and high-speed responsiveness, and allows a light emitting device to be reduced in thickness and weight.
Meanwhile, the organic light emitting device is broadly classified into a fluorescent light emitting device and a phosphorescent light emitting device depending on the kind of excitons involved in emission. In particular, the phosphorescent light emitting device is an electronic device including a phosphorescent light emitting material in an organic compound layer, specifically a light emitting layer, which constructs the organic light emitting device, in which triplet excitons are involved in emission. Here, the phosphorescent light emitting material is excited to the triplet state through the recombination of holes and electrons, and emits phosphorescent light when returning to the ground state. Thus, the phosphorescent light emitting device is an organic light emitting device which provides emission derived from the triplet excitons.
Further, the phosphorescent light emitting device has attracted attention in recent years because the internal quantum efficiency of the phosphorescent light emitting device is four times as large as the internal quantum efficiency of the fluorescent light emitting device in theory. However, in the phosphorescent light emitting device, there is a room for further improvement in emission efficiency.
Meanwhile, there are various proposals concerning materials to be used in the phosphorescent light emitting device. Here, a material for constructing a hole transport layer included in the phosphorescent light emitting device is exemplified by the following compounds A and B disclosed in PTL 1.
